Over the weekend, a Japanese auction site revealed an incredibly rare version of Nintendo's Wii remote: one that was designed not for a Wii console, but for the previous generation's GameCube. And at least one game developer has already attested to its legitimacy.

The previously unrevealed remote controller, which sold at Yahoo Auctions for 74,000 yen (approximately $663 USD) on Thursday, looks incredibly similar to what eventually launched for the Wii, arstechnica.com reported.

The button layout and shape of the remote looks quite similar, and it includes a paired ‘nunchuk’ controller and sensor bar. But unlike the wireless Wii controller that eventually launched in 2006, this one is hardwired — and includes a GameCube controller connector at the end of its apparently long cord.

The attached prototype nunchuk looks even more like its Wii sibling, with its biggest difference being an Ethernet cable as its connector. This was eventually replaced by a proprietary Wii controller connector (which is still used to this day for Nintendo's ‘classic’ miniature consoles).

This prototype also relies on a ‘sensor bar’ that emits infrared lights for the remote to track. The auction listing included this bar, which has a pair of bulges at its edges, measures larger than the retail Wii sensor bar, and plugs into the GameCube via its memory card slot.

Its connector looks a lot like a GameCube memory card, and the auction's buyer, Twitter user ‘smprp’, posted some very clear photos of that authentic-looking connector (embedded above).

But if the whole thing still looks like a fake to you, WayForward game development director James Montagna used his Twitter account on Saturday to confirm the controller's legitimacy: "I remember seeing these back when it was still known as the Nintendo Revolution!" he wrote.

Montagna's memory was jarred in particular by noticing something interesting about the older Wii remote's d-pad and primary buttons: That they were lifted wholesale from the Game Boy Advance SP.

Montagna went on to post images he held onto during his work on early Wii software, showing off other prototype versions of the Wii remote.

His images were closer to the final product, only with a slightly different size and the ‘plus’ and ‘minus’ buttons still being labeled with text as ‘start’ and ‘select’, respectively. And in one shot, taken from E3 2006, those buttons had ‘pause’ and ‘back’ icons. Those were later changed to pluses and minuses.

Nintendo has previously shown off prototype controllers made when the system was still named the Nintendo Revolution, and these ranged from Wii-like remotes to GameCube-like controllers to even a giant, single-button controller.

This weekend's revelation appears to be something offered to developers during the final stretch of pre-Wii development, perhaps when game makers were combining the new controller type with existing GameCube development kits. The auction's winner has not yet been able to get the GameCube Wiimote working on any of the hardware he owns, nor has he unscrewed the controller to determine whether it has identical accelerometer hardware inside.